1. Field of the Invention
This invention relates to a control system for a clutch and more particularly to a control system for a fluid activated clutch which utilizes a clutch oil shut-off valve.
2. Description of the Prior Art
Motorized vehicles and machinery, including those used in agricultural and industrial type equipment, have one or more clutches which are actuated by fluid pressure in order to transfer torque between the power source and the output. For safety reasons, a control system is often provided with an electric switch which requires selection of either a neutral or a park position before the vehicle or machinery can be started. The purpose of this switch is to prevent the vehicle or machinery from being started until the operator is in a safe position. However, the use of such electric switches makes it possible for an operator to short across the switch thus circumventing its usefulness. For example, if an operator jump-starts a vehicle, which has been left in gear, he may be tempted to bypass the neutral start switch and upon starting the engine, the vehicle will move either forward or in reverse. This unexpected movement could cause the vehicle to strike and possibly injure an unsuspecting person. In order to alleviate such occurrences, several hydraulically activated control systems have been devised which utilize multiple clutch activated valves which have to be activated before the vehicle can be driven. Two such patents in this area include
U.S. Pat. No. 3,863,523 issued February 1975 to J. Starling et al and U.S. Pat. No. 3,468,194 issued September 1969 to J. Horsch et al. The Starling patent teaches a transmission control system having controls for engaging both speed ratio devices and directional devices. A safety valve is present which functions to insure that initially no fluid can be supplied from a fluid source to the speed ratio device unless the directional device control is in a neutral position. The safety valve shifts only after a build-up of pressure is present in the chosen speed ratio device. Such safety valve allows full pressure buildup in the speed ratio device and also allows full pressure to be supplied to the chosen directional drive device upon shifting of the directional drive control from the neutral position. The Horsch patent is just as complicated in its use of multiple valves. In this patent, a transmission control system is taught to control fluid pressure and fluid flow. The control system has speed selector valves for providing hydraulic fluid to selectively actuate speed and directional gear clutches and a pressure modulating valve for modulating pressure rise of the hydraulic fluid. A differential valve is present which has fluid pressure regulator means to provide fluid to the directional selector valve at a differentially constant lower pressure compared with main rail pressure. This differential valve includes a safety reset valve which prevents actuation of a directional gear clutch after a startup with the controls inadvertently out of neutral gear. The functional complexity and cost of these types of control systems has discouraged their implementation. Now a control system has been invented for a vehicle or a piece of machinery operational which requires activation of only one clutch.